The Red Sox announced the 37-year-old veteran would return to the team with a two-year deal reported by ESPN to be worth at least a $26 million.
"I want to really thank the ownership for approaching me and letting me know that they want me back," Ortiz said. "They went straight up to me and let me know what they were planning on doing, and that got me more than confident walking into the off-season knowing that I was going to be a Red Sox."
Ortiz, who batted .318 with 23 homers and 60 RBIs in only 90 games in 2012, missed most of the second half of the season with a right Achilles injury.
Valentine made comments last month suggesting Ortiz didn't return because the last-place Red Sox were out of the playoff hunt, but Ortiz told ESPNDeportes.com that was untrue.
"Stopping me [from playing] was the decision of the doctors, management, the manager and me," he said. "The team doctor recommended that I stop playing to not make the situation worse for the tendon."